There are various processing problems associated with both separating delicate essential volatiles from edible substrates and extracting soluble solids from such substrates. See U.S. Pat. No. 3,821,447, June 28, 1974 to Jasovsky et al., and U.S. Pat. Pat. No. 3,717,472, Feb. 20, 1973 to Strobel.
For example, take roast and ground coffee. Prewetting a charge of roast and ground coffee with water is known in the art. For prewetting in steam-stripping processes see Clinton et al., U.S. Pat. No. 3,244,531, Apr. 5, 1966, and Cascione, U.S. Pat. No. 3,532,507, Oct. 6, 1970, both assigned to the General Foods Corporation.
Prewetting of roast and ground coffee in extraction processes is also known in the art. For example, see Patel U.S. Pat. No. 3,549,380 and Sivetz and Foote, Coffee Processing Technology, Avi Publishing Company, 1963, Vol. 1, page 338, both of which are incorporated herein by reference.
Patel discloses a process of uniformly wetting roast and ground coffee during the loading of the coffee into an extraction column for capacity and processing improvements.
The Sivetz reference teaches that prewetting has the advantages of improving cup flavor, assisting in gas liberation from the disrupted cells of the roast and ground coffee, reducing the channeling of fines during the extraction process, and contributing to lower frequencies of excessive pressure drops.
Additionally, the Sivetz reference says that prewetting can be done outside of the extraction column but further notes that this practice is bad "because it causes staling of ground coffee in less than an hour, accompanied by a heavy undesirable flavor and a loss in natural coffee volatiles." Sivetz teaches that prewetting of roast and ground coffee within the extraction columns subsequent to loading allows more fresh coffee solubles to be released before hydrolysis products and tars are pushed through the system.
Kappenberg et al. in U.S. Pat. No. 2,340,758 discloses prewetting by uniformly distributing prewetting liquid through the coffee mass "as by spraying it with agitation." The Kappenberg et al. reference teaches prewetting outside of the extraction column previous to loading and thereafter the wetted coffee after swelling is transmitted to the extraction chamber where it is packed either by hand or mechanically. This process, according to Kappenberg et al., is described to have the advantage of continuous operation without channeling, clogging, buildup of high back pressures and the like, and also the attendant advantage of high throughput. The patent notes that as a result of the prewetting more finely ground coffee can be used. The patent further notes that it is not feasible to prewet the fresh roast and ground coffee in the extraction chamber because it cannot be evenly wetted and, more seriously, it expands when wetted within the restricted space causing the formation of dense masses and consequent jamming of the columns.
As shown by these several prior art references, there are certain advantages in prewetting after entry into a suitable vessel or extraction column and certain advantages in prewetting before entry into the vessel. However, as shown by the teachings of these references, both prewetting prior to placement in the vessel and prewetting after placement in the vessel also have accompanying disadvantages. If the prewetting is done prior to placement of the roast and ground coffee in an extraction column, the grind size of the roast and ground coffee must be smaller to compensate for the swelling of the coffee particles which naturally occurs upon wetting. The swelling of the coffee particles, as one would expect, increases their volume and thereby decreases the load capacity of the extraction column. Decreasing the load capacity of the extraction column decreases the throughput of the column and thereby lessens extraction efficiency.
Prewetting inside of the reaction vessel, as shown in these several references, has several disadvantages. For example, once the roast and ground coffee is packed inside the reaction vessel or extraction column, as the case may be, prewetting of said coffee in a uniform manner was heretofore believed to be a practical impossibility. As a result, some of the coffee particles are prewetted and swell and others are not contacted with the prewetting liquid and, therefore, do not swell. This non-uniform prewetting causes large pressure drops across the reaction vessel which often results in channeling and clogging of the reaction vessel and necessitates a complete shutdown followed by a time-consuming cleaning process.
Additionally, prewetting inside of the vessel heretofore necessitated the use of lower levels of coffee fines which, in turn, decreased product yield. Coffee fines, as the term is used herein, is defined as roast and ground coffee capable of passing through a 20 mesh U.S. Standard Screen. The reason that less coffee fines can be used if prewetting inside of an extraction column or distillation vessel is practiced is because the prewetting is not uniform and oftentimes the fines are not contacted with the prewetting liquid. Because the fines are not contacted with the prewetting liquid, they do not exhibit the usual swelling phenomena associated with prewetting. Thus, the unwetted fines tent to remain at their non-prewet original sizes and as they agglomerate during steaming or extraction they tend to clog the vessels, causing a buildup of back pressure which, in turn, necessitates a shutdown and cleaning process.
Prewetting the coffee particles prior to, or during, loading of the coffee particles into a reaction vessel has been practiced to avoid some of the above-mentioned problems. However, prewetting outside the column causes staling of roast and ground coffee in less than an hour, accomplished by the development of a heavy, undesirable flavor. Also, if the coffee particles are to be subjected to a steam distillation operation before aqueous extraction, such prewetting prior to, or during, loading is unfeasible. This is because the steam distillation process, by its very nature, tends to desorb the most volatile essentials upon the coffee particles' initial contact with moisture during steam distillation. Thus, prewetting the coffee particles before they are secured inside the vessel results, in effect, of releasing the most volatile, and often the most desirable, essentials from the coffee particles before the steam distillation operation is commenced.
Consequently, it would be desirable to be able to add the coffee particles to the extraction column in a non-moist condition to preserve the more highly volatile flavor and aroma components for steam distillation thereof, but yet avoid the processing problems encountered when dry coffee particles are loaded in a conventional extraction column.
The present invention affords the major advantages of prewetting outside of the reaction vessel, prewetting during loading, and prewetting inside the reaction vessel without the attendant disadvantages of either process. Pressure drops and backup pressure are no longer a problem, the percentages of fines employed can be higher or all fines can be employed.
The present invention includes improvements in this type of process which permits high yields, i.e., substantially complete devolatilization and/or extraction of the essential volatiles and/or extractable constituents of the substrate without channeling, clogging, building up of pressure drop and the like; high output from the given apparatus at low cost, and the production of a product of consistently high concentration and quality.